div.chamado {
    width: 500px;
    height: 300px;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-left: -250px;
    margin-top: -150px;
    z-index: 1;
}

div.vaga {
    position: absolute;
    z-index: 2;
    background-color: blue;
	filter:alpha(opacity=50); 
	opacity:0.5;
}